Write performance compared to Postgresql

[Jeff Williams]

Hi,

I am looking at cassandra for a logging application. We currently log to a 
Postgresql database.

I set up 2 cassandra servers for testing. I did a benchmark where I had 100 
hashes representing logs entries, read from a json file. I then looped over 
these to do 10,000 log inserts. I repeated the same writing to a postgresql 
instance on one of the cassandra servers. The script is attached. The cassandra 
writes appear to perform a lot worse. Is this expected?

jeff@transcoder01:~$ ruby cassandra-bm.rb 
cassandra
  3.170000   0.480000   3.650000 ( 12.032212)
jeff@transcoder01:~$ ruby cassandra-bm.rb 
postgres
  2.140000   0.330000   2.470000 (  7.002601)

Regards,
Jeff


require 'rubygems'
require 'cassandra-cql'
require 'simple_uuid'
require 'benchmark'
require 'json'
require 'active_record'

type = 'postgres'
#type = 'cassandra'
puts type

ActiveRecord::Base.establish_connection(
  #:adapter => "jdbcpostgresql",
  :adapter => "postgresql",
  :host => "meta01",
  :username => "postgres",
  :database => "test")

db = nil
if type == 'postgres'
    db = ActiveRecord::Base.connection
else
    db = CassandraCQL::Database.new('meta01:9160', {:keyspace => 'PlayLog'})
end

def cql_insert(table, key, key_value)
  cql = "INSERT INTO #{table} (KEY, "
  cql << key_value.keys.join(', ')
  cql << ") VALUES ('#{key}', "
  cql << (key_value.values.map {|x| "'#{x}'" }).join(', ')
  cql << ")"
  cql
end

def quote_value(x, type=nil)
  if x.nil?
    return 'NULL'
  else
    return "'#{x}'"
  end
end

def sql_insert(table, key_value)
  key_value.delete('time')
  cql = "INSERT INTO #{table} ("
  cql << key_value.keys.join(', ')
  cql << ") VALUES ("
  cql << (key_value.values.map {|x| quote_value(x) }).join(', ')
  cql << ")"
  cql
end

# load 100 hashes of log details
rows = []
File.open('data.json') do |f|
  rows = JSON.load(f)
end

bm = Benchmark.measure do
  (1..10000).each do |i|
    row = rows[i%100]
    if type == 'postgres'
        fred = sql_insert('playlog', row)
    else
        fred = cql_insert('playlog', SimpleUUID::UUID.new.to_guid, row)
    end
    db.execute(fred)
  end
end
puts bm